Which action is an appropriate security measure when the aircraft is unattended?

• A. Increase flight altitude
• B. Leave radios on
• C. Leave doors unlocked
• D. Disable engines

Answer: (D)

When an aircraft is unattended, the priority is to prevent unauthorized access or accidental start. Disabling the engines achieves this most effectively because it makes the propulsion system inoperable, so the aircraft cannot be started or moved by someone else. It directly stops a potential misuse path and signals that the aircraft is secured.

Other actions don’t improve security and can create new risks. Increasing altitude isn’t a security measure and could introduce safety concerns; leaving radios on wastes power and could reveal location or status; leaving doors unlocked directly exposes access points to tampering. So disabling the engines is the best security measure when the aircraft is not attended.